Research On The Behavior Of Rectangular Concrete Columns Strengthened With CFRP Sheets

Experimental and analytical studies in this paper are focused on rectangular columns strengthened with Fiber-Reinforced Polymer materials. A new hybrid strengthening method is proposed for the problem of non-effective confinement area in rectangular section, which was tested successfully.At present, researches on strengthened rectangular columns are few. To study the behavior and damaged properties of rectangular columns strengthened with CFRP sheets, 18 specimens are designed and tested in this paper, which are changed from completely rectangular to circular section. Effect of section shape and plies of CFRP sheets on the behavior of columns are studied. The effective strain of CFRP sheets is studied also. So many data was got for research on compression properties of CFRP strengthened rectangular columns.Under axially loading, the confinement of FRP materials for rectangular columns is not as effective as for circular ones due to the limit of section shape. According to the analytical model combined with numerical results, the relationship between confinement stress and corner radii is studied. It is also studied that the influence of concrete dilation in rectilinear part of rectangular section on the strain of Carbon FRP(CFRP) sheets. The new confinement area models and shape factor models are proposed. Taking the effective strain factor into account, the formula is developed about the effective lateral confinement pressure for strengthened concrete columns with CFRP sheets. The new models about compressive strength and its corresponding strain are proposed, and a new stress-strain model of the CFRP fully-confined rectangular column is developed to simulate the whole curve of the tested specimens, which is tested with the test results.It is always a practical requirement to use CFRP materials to strengthen Reinforced-Concrete(RC) columns. It also influenced the carrying capacity of the RC columns. The discontinued CFRP materials are often used to strengthen RC columns. The formula about effective confinement pressure produced by discontinued FRP materials is developed. By considering different territory of different confinement materials, the effect of stirrups and longitudinal reinforcements, the compressive strength of CFRP strengthened RC columns can be calculated with the newly developed model.